1. Field of the Invention
The present invention relates to a chain lever hoist and, more particularly, to a chain lever hoist wherein a load sheave is rotated to wind up and down a load chain passing over the load sheave by the reciprocating operation of an operating lever.
2. Description of the Prior Art
Known as a chain lever hoist of this type is, for example, the one disclosed in Japanese Patent Publication No. 54(1979)-9381 and shown in FIG. 10.
As shown in FIG. 10, in the chain lever hoist, a load sheave 4 over which a load chain 3 passes in engaging relation is supported in rotatable relation between spaced apart first and second side plates 1 and 2 via two bearings 5, 6. The load sheave 4 has a shaft bore in which a drive shaft 7 is inserted in rotatable relation, and a mechanical brake 8 is provided on the drive shaft 7 at the outside of the second side plate 2.
The mechanical brake 8 comprises a second hub 11 connected to the drive shaft 7 in non-rotatable relation relative thereto and having a cylindrical portion 9 and a flange 10, an anti-reverse gear 12 supported on the cylindrical portion 9 of the second hub 11 in freely rotatable relation, two lining plates 13 and 14 supported on the cylindrical portion 9 of the second hub 11 at opposite sides of the anti-reverse gear 12, and an anti-reverse pawl 16 pivoted to a pawl shaft 15 projecting from the second side plate 2 and so biased as to be engaged with the anti-reverse gear 12.
A first hub 17 having engaging teeth 21 around an outside thereof is threadedly mounted on the drive shaft 7 at the axial outside (at the right side as viewed in FIG. 10) of the mechanical brake 8. An operating handle 18 is fitted onto the drive shaft 7 and is fixed to the first hub 17 with screws 19, 20 so as to be non-rotatable relative thereto at the axial outside of the first hub 17. Further, a coil spring 28 for biasing the first hub 17 and the second hub 11 to be forced away from each other is interposed between the first hub 17 and the second hub 11.
A lock nut 30 is fixed to the drive shaft 7 by a set pin at an end of the drive shaft 7 on the side thereof on which the operating handle 18 is fitted, with a predetermined spaced interval from the operating handle 18, so as to be axially immovable, and thereby the range of axial movement of the first hub 17 movable together with the operating handle 18 is limited. On the other hand, a reduction gear mechanism 24 is provided at the other axial end of the drive shaft 7, to transmit the drive applied from the drive shaft 7 to the load sheave 4 at a predetermined reduction ratio.
A gear cover 25 for covering the reduction gear mechanism 24 is fixed to the first side plate 1, and a brake cover 26 for covering the mechanical brake 8, formed having an opening 29 for the first hub 17 to be fitted in, is fixed to the second side plate 2. An operating lever 22 is loosely fitted around the outside of the first hub 17 at the axial outside of the brake cover 26. The operating lever 22 is provided with an engaging pawl 23 which can be selectively switched to a normal position at which only a normal rotation drive of the operating lever 22 is transmitted, a reverse position at which only a reverse rotation drive of the operating lever is transmitted, and a neutral position at which the engaging pawl 23 and the engaging teeth 21 are not engaged with each other, to disengageably engage with engaging teeth 21 of the first hub 17.
When a load is hoisted up by use of the chain lever hoist thus constructed, the engaging pawl 23 of the operating lever 22 is first switched to the normal position by the operation of a selector lever 27 to be brought into engagement with the engaging teeth 21 of the first hub 17 and, then, the operating lever 22 is reciprocated to screw the first hub 17 forward so as to press the mechanical brake 8, whereby the load sheave 4 is allowed to rotate in the normal rotation direction through the drive shaft 7 and the reduction gear mechanism 24. On the other hand, when the load is lowered down, the engaging pawl 23 of the operating lever 22 is first switched to the reverse position by the operation of the selector lever 27 to be brought into engagement with the engaging teeth 21 of the first hub 17 and, then, the operating lever 22 is reciprocated to screw the first hub 17 backward, so as to release the mechanical brake 8, whereby the load sheave 4 is allowed to rotate in the reverse rotation direction under the weight of the load to permit the lowering of the load. Along with the lowering of the load, the drive shaft 7 is reversed, so that the first hub 17 is screwed forward again to put the mechanical brake 8 into action. By repetition of this action and release of the mechanical brake 8, the load can be gradually lowered down.
Further, when the load chain 3 is desired to be adjusted in length at the start of working, for example, the engaging pawl 23 of the operating lever 22 is switched to the neutral position by the operation of the selector lever 27, not to be brought into engagement with the engaging teeth 21. Then, the pressing of the first hub 17 against the mechanical brake 8 is released by a spring force of the coil spring 28 and, as a result of this, the first hub 17 comes to be rotatable together with the drive shaft 7 to thereby produce the free rotation condition. If a load is suspended from the load chain 3 on the loaded side, a large thrust from the weight of the load is applied to the drive shaft 7, so that even if the engaging pawl 23 is switched to the neutral position, since the first hub 17 presses the mechanical brake 8 against the spring force of the coil spring 28, the free rotation state will not be produced.
However, when the free rotation operation of the chain lever hoist thus constructed is carried out, since the first hub 17 and the operating handle 18 are in contact with the operating lever 22, the contact resistance can hinder smooth rotation of the first hub 17 to cause the first hub 17 to rotate relative to the drive shaft 7 and, as a result of this, there may be produced a possible problem that the first hub 17 may press the mechanical brake 8 to put the mechanical brake 8 into action.
On the other hand, it may be practical to allow for the contact resistance between the first hub 17 and the operating handle 18 and the operating lever 22 and use the coil spring 28 having a spring force sufficient for the first hub 17 to rotate against the contact resistance. However, it is hard to pre-select the coil spring 28 having the right spring force corresponding to the contact resistance. Besides, since the contact resistance varies depending on the degree of abrasion or wear of the contacting parts, the rotation of the first hub 17 varies depending on the degree of the abrasion or wear. Further, the chain lever hoist is used in various conditions, such as the condition in which the chain lever hoist is suspended from overhead and the operating lever is in vertical orientation, the condition in which the chain lever hoist is suspended from overhead and the operating lever is in somewhat tilt with respect to the vertical direction, or the condition in which the chain lever hoist is not suspended from overhead and is put in horizontal orientation. Depending on the use condition of the chain lever hoist, variation is caused in the application of the weight of the first hub 17, the operating handle 18 and the operating lever 22, which in turn causes variation in the contact resistance in each use condition. Because of this, the ability for the first hub 17 to be rotated relative to the drive shaft 7, in other words, the ability for the mechanical brake 8 to be engaged in the free rotation state, is varied and, therefore, there is the disadvantage that a stable free-rotation operation cannot be attained.
It is the object of the present invention is to provide a chain lever hoist that can attain a stable free-rotation operation for a long term with simple design.
The present invention provides a chain lever hoist comprising a load sheave with which a load chain is engaged; a first hub forming engaging teeth around an outside thereof; an operating lever having an engaging pawl detachably engageable with the engaging teeth and loosely fitted around the outside of the first hub; a mechanical brake comprising a second hub interposed between the first hub and the load sheave, an anti-reverse gear supported on the second hub, two brake disks supported on the second hub at the opposite sides of the anti-reverse gear, and an anti-reverse pawl disposed at the outside of the anti-reverse gear and engageable with the anti-reverse gear; a drive shaft, on which the first hub is threadedly mounted and with which the second hub is connected in non-rotatable relation relative thereto and onto which the load sheave is fitted, for allowing drive applied from the operating lever to be transmitted to the load sheave through a reduction gear mechanism; a biasing means, interposed between the first hub and the second hub, for biasing the first hub and the second hub to be away from each other, the biasing means having a biasing force of such an extent that can keep the mechanical brake in its released state during free rotation operation and also put the mechanical brake into action in the free rotation operation when a rotation drive exceeding contact resistance between the drive shaft and the first hub is applied to the drive shaft; and a brake cover for covering the mechanical brake, the brake over being formed having an opening for the first hub to be inserted in, wherein when engagement between the engaging pawl and the engaging teeth is released in the state in which no load is applied to the load chain on a loaded side thereof, pressing of the first hub against the mechanical brake can be released by the biasing force of the biasing means to put the first hub and the drive shaft into a rotatable-together state to thereby produce free rotation condition and wherein the operating lever is rotatably supported on the brake cover at the opening thereof with a predetermined spaced interval from the first hub.
In this arrangement, the operating lever is rotatably supported on the brake cover at the opening thereof with a predetermined spaced interval from the first hub. Thus, the first hub is rotated together with the drive shaft without contacting with the operating lever, thus ensuring smooth and reliable rotation of the first hub. By virtue of this, the condition for the relative rotation of the first hub to the drive shaft to be caused, in other words, the condition for the mechanical brake to be put in action in the free rotation state, can be determined by only the biasing force of the biasing means. Thus, it is good enough for attainment of the reliable free rotation operation to adopt the biasing means having a biasing force of such an extent that can put the mechanical brake into action when the rotation drive exceeding the contact resistance between the drive shaft and the first hub is applied to the drive shaft in the free rotation state. Thus, the stable free rotation operation can be ensured for a long term with the simple design.
According to the present invention, it is preferable that the chain lever hoist further comprises an operating member fitted onto the drive shaft and mounted on the first hub in non-rotatable relation relative thereto and that a cylindrical insertion portion for inserting therein the operating member is formed in the operating lever, with a predetermined spaced interval from the operating member.
In this arrangement, the pressing of the first hub against the mechanical brake can be released simply by rotating the operating member in the reverse direction for the free rotation operation, and as such can facilitate the free rotation operation. Also, since the operating member is mounted on the first hub with a predetermined spaced interval from the cylindrical insertion portion of the operating lever, the operating member can be prevented from contacting with the operating lever during the free rotation operation, and as such can ensure the smooth and reliable rotation.
According to the present invention, it is preferable that the brake cover has a brake-cover-side connecting portion for connecting the brake cover with the operating lever, while on the other hand, the operating lever has a lever-side connecting portion for connecting the operating lever with the brake cover, that the brake-cover-side connecting portion and the lever-side connecting portion are connected together by connecting means, and that the connecting means is arranged with a predetermined spaced interval from the first hub.
In this arrangement, since the operating lever and the brake cover are connected with each other by the connecting means arranged with a predetermined spaced interval from the first hub, the axial movement of the operating lever and the brake cover are limited, while also improved strength of the connecting portion thereof can be attained. By virtue of this, the operating lever can be kept from contacting the first hub and the operating member due to a tilted orientation of the operating lever resulting from the reciprocating motion of the operating lever, for example. Thus, a further stable free rotation operation can be attained.
According to the present invention, it is preferable that the connecting means comprises a holding member for holding the brake-cover-side connecting portion and the lever-side connecting portion in sandwich relation and a retaining member which is held in sandwich relation together with the brake-cover-side connecting portion and the lever-side connecting portion.
In this arrangement, the retaining member is fitted in the holding member and also the lever-side connecting portion and the brake-cover-side connecting portion are fitted by the retaining member, whereby the operating lever can be rotatably supported on the brake cover.
By virtue of this, for example the mount of the operating lever on the brake cover can readily and surely be attained by the use of the holding member arranged in advance, without taking such a step that after the brake-cover-side connecting portion and the lever-side connecting portion are held in sandwich relation by the holding member, the holding member is crimped.
According to the present invention, it is preferable that the drive shaft has a screw-thread portion, for the first hub and the second hub to be both threadedly mounted on, which is formed being substantially equal in diameter, and a fitting groove formed in the screw-thread portion at a certain point thereof, whereby the first hub and the second hub are threadedly mounted on the screw-thread portion and also a limiting means is fitted in the fitting groove so that an axial movement of the second hub can be limited.
In this arrangement, since the screw-thread portion on which the first hub and the second hub are both threadedly mounted is formed being substantially equal in diameter, rigidity of the drive shaft can be increased and thus durability of the chain lever hoist can be increased. For example in a case where the drive shaft is splined at a portion thereof for mounting the second hub thereon and is threaded at a portion thereof for mounting the first hub thereon, the drive shaft will inevitably be reduced in rigidity and durability. This is because since the second hub must be mounted first prior to the mounting of the first hub in the assembling work, the threaded portion of the drive shaft cannot help being made smaller in diameter than the splined portion and also a portion of the drive shaft extending between the splined portion and the threaded portion cannot help being made smaller in diameter than those portions for the machining need. The arrangement of the invention in which the first hub and the second hub are threadedly mounted on the screw-thread portion of substantially equal in diameter and also the limiting means is fitted in the fitting groove, whereby the first hub can be screwed forward and backward along the drive shaft and also the second hub can be non-rotatable relative to the drive shaft can provide increased rigidity of the drive shaft and thus improved durability of the chain lever hoist.